DAIRY FARMING DAIRYING. 73 



tion is not the temperature at which chemical changes talie place In storage 

 butter, the identity of the iodoform reacting substances could without doubt 

 be ascertained. Whether the small amounts of iron ordinarily present in but- 

 ter can slowly bring about the same kind of a change that larger amounts of 

 iron bring about in milk in a very much shorter time is to be determined by 

 future investigation." 



Butter made from cream to which copper sulphate had been added showed 

 a fishy flavor after a storage of 40 days, and after 3 months of storage a de- 

 cided mackerel flavor. One experiment was made with cream ripened in 

 contact with 2 sheets of bright copper, and another in wliich the cream came 

 in contact with a large surface of copper for a short time. Fishy flavors 

 developed in both cases. Both tests showed very plainly " the deteriorating 

 effect of poorly tinned pasteurizers, for aside from this all other conditions were 

 exactly alike during the complete process of butter manufacture. Considering 

 the short duration of contact, the change in the flavor of the butter even when 

 fresh is very marked. The efl;ect of copper even in small amounts seems to 

 cause more marked changes in butter flavor than iron, with a marked tendency 

 toward a flshy flavor in storage." 



A study of the bacteria which survive pasteurization, S. H. Ayers and 

 W. T. Johnson, Jr. (U. S. Dept. Agr., Bur. Aiiini. Indus. Bui. 161, pp. 66, flgft. 

 50).-^A study of bacteria which survive the temperature at which milk is 

 usually pasteurized, undertaken since those which survive form the foundation 

 for subsequent bacterial development. 



In reply to circular letters it was found that the temperatures at which milk 

 is usually pasteurized are extremely variable. " The average temperature used 

 throughout the country with the 'holder' process is 62.8° C. (145° F.), with 

 the 'flash' process, 71.1° C. (160° F.). 



"Reports from 219 milk plants show that 75 used the 'holder' and 144 the 

 'flash' process. The range in temperatures is from 60° C. (140° F.) to 82.2° C. 

 (180° F.). Of the plants using the 'holder* process only 1.3 per cent employ 

 temperatures too low for proper pasteurization. Of those which use the ' flash ' 

 process approximately 42 per cent use temperatures too low to be effective." 



iMost of the experiments of the authors were made at temperatures of 62.8° C. 

 for 30 minutes, as this was the average temperature for the " holder " process. 

 Higher temperatures in some cases were used in order to show changes in the 

 I'acterial groups which survived. 



Percentage bacterial reduction is considered of no value in determining the 

 efficiency of the process of pasteurization. As a general rule when the bacterial 

 content of raw milk is high there will be a high percentage reduction and vice 

 versa when the bacterial content is low. 



"A heating period of 3 hours causes a marked increase in the reduction of 

 bacteria in milk over one-half hour's heating, when a temperature of 54.4° C. 

 (130° F.) and 57.2° C. (135° F.) are used. At 60° C. the increased reduction 

 is much less. According to the results of one experiment in this investigation, 

 a 6 hours' period of heating at 62.8° C. does not produce any more destruction 

 of bacteria than does one-half hour's heating. 



" Sudden cooling from 62.8° or 71.1° C. within 15 seconds to from 1.7°-3.9° C. 

 (35°-39° F.) does not cause any destruction of bacteria. The long-prevailing 

 idea that sudden cooling is an essential part of the process of pasteurization is 

 erroneous so far as any increased destruction of bacteria is concerned. Its 

 value lies only in the fact that milk suddenly cooled is not allowed to stand at 

 temperatures between 37.8° C. (100° F.) and 10° C. (50° F.), where rapid 

 bacterial development might occur. 



